Skin provides an important barrier against infectious agents such as bacteria, viruses, parasites and the like, as well as dangerous or toxic materials, and the dangerous effects of mechanical trauma, damage by ultraviolet light and the like. Damaged skin, however, may not only fail to provide such a barrier, but may itself become infected or otherwise prevent the body from heating the damaged area naturally. For certain types of injuries, such as burns or chronic wounds, for example, where the damaged tissue may be dead, it must be removed in order for the injury to heal and prevent future complications.
Therefore, for these types of injuries, a process known as “debriding” the damaged skin has been developed. The goal of the debriding process is to remove the damaged skin, with minimal or no damage to the healthy surrounding skin and also the layers of tissue below the damaged skin. The damaged skin may itself actually include dead tissue, which as used herein, includes diseased tissue, necrotic tissue and eschar. Eschar is tissue that has been damaged, burned (from thermal, chemical or electrical burn causes, for example) or from ischemia (pressure sores, diabetes or peripheral vascular disease ulcers, for example). Without debridement, bacterial infection of the dead tissue and even sepsis may occur, leading to sloughing of the damaged tissue, often with the initially undamaged tissue becoming compromised by the infection of the dead tissue. This process may lead to death of the patient. If the patient survives and recovers, the delayed healing of the damaged tissue area may cause the development of granulation tissue that eventually forms disfiguring scar tissue, which lacks flexibility as well as other physiological functions and cosmesis (appearance), which are features of healthy skin.
The eschar related complications are so important that the earliest debridement is the standard of care of any necrotic skin area. The debriding process is currently performed with physical or mechanical removal (excision) of the dead tissue, which is clearly disadvantageous because of the potential for damage to healthy tissue, both surrounding the dead tissue and also present below this tissue. For example, for surgical debridement with special knives called dermatomes, it is estimated that up to 30–50% of healthy tissue may be sacrificed during the debriding procedure. The mechanical—surgical debridement process requires a certain level of surgical skills that may not always be available. Mechanical debridement is also painful, requiring local or systemic analgesia. Therefore, the background art has focused on non-mechanical debriding processes, and also mechanical or physical processes which may be more precisely focused in order to avoid damage to healthy tissue.
For example, H. J. Klasen in “A review on the non-operative effect of necrotic tissue from burn wounds”, Burns 26 (2000), 207–222, reviews non-surgical treatment of burn wounds, and describes enzymatic and chemical debriding agents, such as proteolytic enzymes and enzymes of plant origins. The review concludes that although enzymatic debridement would appear to be a useful and attractive form of treatment, it unfortunately suffers from highly variable results.
PCT Application No. WO 98/53850 also teaches the use of chemical debriding agents such as enzymes for the treatment of burned skin. However, such chemical debriding agents alone may not prove sufficiently effective for all burn or other eschar situations.
With regard to physical mechanisms for debridement, the background art includes teachings on the use of ultrasound for such debridement. For example, S. F. Schoenbach et al., in Plastic and Reconstructive Surgery, July 1980, 66(1), pp. 34–37, describe experiments performed on rats for reducing the bacterial count of infected full-thickness burn wounds by ultrasonic treatment.
PCT Application No. WO 98/32379 describes an ultrasound system for treatment of neoplastic or precancerous skin tissue. The ultrasound generating element is coupled to a container holding a liquid medium capable of transmitting ultrasound waves, which is preferably a degassed solution such as water. The solution may also contain substances that are activated by ultrasound to release free radicals. However, the use of an independently therapeutic or active solution is not taught or suggested by this reference.
Other uses of ultrasound for skin treatment have been described in French Patent Application No. 2,762,791, which discloses a probe for the simultaneous application of ultrasound and electrical current to the skin; U.S. Pat. No. 4,372,296, which describes a method of treating acne with ultrasound; and U.S. Pat. No. 5,656,015 describes an ultrasonic therapeutic system for the treatment of soft tissue. Again, these references are not focused on the removal of dead tissue.